foundations

Why git add . is a trap, what a commit stores, and why a deleted secret is still in your history. The local half of Git, before any remote.

Why a long job ignores your Ctrl-C, and the handler that fixes it. Signals, the child processes a script leaves running, and the init that inherits them.

The same backup script, grown from four lines that look fine to one you can trust to fail without eating your last good backup. Quoting, exit codes, set -euo pipefail and traps, with the reason behind each line.

From the universal chmod -R 777 to a directory only the service can touch. Ownership as a number, the rwx bits, and the setgid, sticky and setuid bits the hardened container leans on.